UNI PUSH-IN BREATHER FILTER 1/2". Connect to the 1/2" 90 degree tube that equalizes pressure under the diaphragm to atmospheric. Regardless of the notation on the package to the contrary, Uni Filter Oil should be applied in the under-diaphragm vent application.
This is a legacy product. If you have one of these already, or would still like to use it, we strongly suggest adding an oiled Under Diaphragm Vent Filter Sleeve to improve filtration. However, adding a second layer does make the assembly less compact.
We recommend purchasing Under Diaphragm Breather Filter MIK0111135110 instead because it achieves better results for less money than the combination UP-123 and filter sleeve.